Gravitational lensing: Deflection of light by the gravitational potential associated with astronomical objects, such as stars, galaxies, and groups and clusters of galaxies. Two distinct regimes are important: (1) strong gravitational lensing, where the gravitational potential is deep enough to produce multiple images of a background source, and (2) weak gravitational lensing, where the gravitational potential distorts the appearance of background sources but does not create multiple images.

Gravitational microlensing: An intensification of light from a background star produced by the gravity of a mass, such as another star or an exoplanet that is aligned almost exactly along the line of sight.

Hubble Space Telescope (HST): Orbiting optical/ultraviolet/near-infrared space telescope launched in 1990 and refurbished at periodic intervals. Current Hubble Space Telescope cameras can image with ∼0.1-arcsecond resolution and take ultraviolet spectra between 1100 and 3000 angstroms.

Hyper Subprime Cam: A camera on Japan’s Subaru optical-infrared telescope, located at the summit of Mauna Kea on the island of Hawaii.

Infrared: Light with wavelength longer than visible light but shorter than radio waves. Near-infrared refers to the wavelength range from ∼1 to 5 microns, mid-infrared is ∼5 to 20 microns, and far-infrared extends from ∼20 microns to ∼200 microns, where the submillimeter begins.

James Webb Space Telescope (JWST): An infrared space observatory under construction, scheduled for launch in 2018 or later, which is the successor to the Hubble Space Telescope.

Kepler: A NASA satellite mission with a photometric monitor of 150,000 stars looking for transits of extra-solar planets ranging in size from Jupiter down to sub-Neptune and Earth-like in radius.

KIlo-Degree Survey (KIDS): A 1,500-square-degree public imaging survey with patches in both the Northern and Southern skies. The survey will use the OmegaCAM instrument mounted on the Very Large Telescope Survey Telescope.

Large Synoptic Survey Telescope (LSST): A priority of the New Worlds, New Horizons (Astro2010) decadal survey, LSST is large aperture, wide field survey telescope and 3,200 megapixel camera to image faint astronomical objects across the sky.

Medium-class (M-class): Medium-scale European Space Agency mission.

Microlensing: See gravitational microlensing.

Near-infrared (NIR): Wavelengths from ∼1 to 5 microns. (Also see infrared).

New Worlds, New Horizons (NWNH): The 2010 National Research Council astronomy and astrophysics decadal survey report, New Worlds, New Horizons in Astronomy and Astrophysics (The National Academies Press, Washington, D.C.).

Optical: Wavelength range of light to which the human eye is sensitive, namely, 3,500 to 8,000 Å.

Pan-STARRS-1: Panoramic Survey Telescope and Rapid Response System, a wide-field (1.8 meter) imaging facility being developed at the University of Hawaii’s Institute for Astronomy.

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